It is known that substituted aminotriazolinones are obtained when corresponding oxadiazolinones are reacted with hydrazine hydrate in water. In U.S. Pat. No. 4,952,701, the oxadiazolinone is initially introduced in water and an excess of hydrazine hydrate is added to the reaction mixture at room temperature. The mixture is then heated and cooked. The excess hydrazine is removed by distillation and the desired aminotriazolinones are obtained. Due to the solubility of the aminotriazolinones in water, the resultant product is obtained in low yields and low purity; and therefore, an additional purification step is required.
Further, it is also known in the art that substituted aminotriazolinones are obtained when corresponding oxadiazolinones are reacted with hydrazine hydrate in the presence of a basic compound and in the presence of a polar organic solvent. Suitable basic compounds are in general inorganic or organic bases or acid acceptors. Such basic compounds include alkali metal or alkaline earth metal acetates, amides, carbonates, hydrogen carbonates, hydrides, hydroxides or alkoxides. Suitable polar organic solvents include dialkyl ethers, dialkyl ketones, nitriles, amides, esters, alcohols, and sulphoxides.
In U.S. patent application Ser. No. 08/696,013, the hydrazine hydrate is initially introduced in the basic compound and the polar organic solvent. The mixture is then heated to the required reaction temperature. As the mixture is cooked, the oxadiazolinone is slowly added until the reaction is complete. The desired aminotriazolinones are obtained by adjusting the pH of the mixture to about 7 by adding an acid and the organic solvent used in the initial step of the process. The solvent and water are removed by distillation and the desired product remains as a residue which is isolated by filtering. However, due to the solubility of the product in water, part of the desired product remains in the water and cannot be recovered. The work-up and isolation of the resultant product is extensive and the product is obtained in low yields.
In these known processes, the use of water or a solvent in the reaction mixture introduces excess water into the reaction and requires extensive purification procedures with resultant low yields. Thus, there is a need for an efficient process for preparing substituted aminotriazolinones, and in particular 4-amino-1 ,2,4-triazolin-5-ones, that produces a high net yield and high purity.